feat(messaging): balanced TOOL parsing, DM shorthand, box.exec, tools.list

- response-harvester: extract [TOOL]/[EXEC] JSON args with balanced-brace
  scanning (']' and nesting inside args no longer truncate calls); add
  [DM {...}] shorthand mapping to dm.send; native aliases (dm, box,
  tools) plus arg-synonym normalization; formatters and expanded hints.
- exec-constrained: new read-only box.exec op (27 allowlisted box-ctl
  reads) and tools.list op backed by --list-ops for dynamic discovery.
- prompt_envelope: advertise dm.send/box.exec/tools.list in every timer
  DM; add dm_call builder.
- lookup_engine + regex_patterns.json: canonical tool_call pattern
  accepts the DM engine, ']' in args, one nesting level.
- tests/test_tool_calls.py: 38 tests; docs/INBAND-MESSAGING-SPEC.md:
  accepted decision record (Final).

bin/lookup_engine.py

@@ -31,7 +31,7 @@ _COMPILED_PATTERNS: Dict[str, re.Pattern] = {}
 # Fallback hardcoded regexes in case files are missing or unreadable
 _FALLBACK_RESULT_RE = re.compile(r"\[RESULT\s+([A-Za-z0-9_/-]+)\]\s*(.*?)(?=\[RESULT\s|\Z)", re.S)
 _FALLBACK_VERB_RE = re.compile(r"\[(ACK|CLAIM|RESULT|DECLINE|NO-ACTION)\s+([A-Za-z0-9_/-]+)\]")
-_FALLBACK_TOOL_RE = re.compile(r"\[(TOOL|EXEC)\s+([a-zA-Z0-9_.-]+)\s+(\{.*?\})\]", re.S)
+_FALLBACK_TOOL_RE = re.compile(r"\[(TOOL|EXEC|DM)\s+(?:([a-zA-Z0-9_.-]+)\s+)?(\{([^{}]|\{[^{}]*\})*\})\]", re.S)
 _FALLBACK_CONTRACT_FOOTER = (
     "Reply: [ACK id] seen | [CLAIM id] mine | "
     "[RESULT id] done | [DECLINE id] | [NO-ACTION id]."